In the taxi or cab service there are constant attempts at rationalization, and computers are coming more and more into the question in this respect as a solution for supervising taxi handling, e.g. for directing the different taxis from the point of view of travelling to suitable pick-up points. Another application may be to take care of the calculation of different tariffs and travelling distances for the cooperating taxis. In such cases it becomes necessary to arrange radio communication between the taxis and a centrally located computer. The probable arrangement in such a system would be that a computer with a radio communication unit is placed centrally in a population center or other region for a given taxi service area. In such a connection it is naturally most rational to allow the computer to carry out all of the calculations of the actual fare as well as statistical information, the computer then also registering information as to selected tariff, distance driven, travelling time, sum due and the like. This means that in the vehicle the taximeter itself would only constitute an indicator unit and a generating unit for tariff information, distance and time. The problem may appear to be easily solved theoretically, but in practice there immediately occur substantial difficulties, which are primarily concerned with the load on the radio communication network in question. All of the taxis running at the same time cannot transmit information continuously on one channel, and a special channel would be needed for each taxi. This is quite impossible from the frequency distribution point of view, and another solution is therefore required. In order to analyze the problem it is suitable to take into account, first of all, the conditions prevailing with respect to a taximeter.
The cost of a fare on a taximeter is generally calculated as the sum of the higher alternative at each instant of a tariff which is based either on time or on distance. The time-dependent tariff is selected automatically when the vehicle speed falls below a given threshold speed, and the distance-dependent tariff when the speed exceeds the threshold speed. In electronic taximeters, this functions so that a constant pulse frequency (clock pulses) is compared with a pulse frequency dependent on road speed. When the speed-dependent frequency is lower than the clock frequency, the journey is debited according to the time-dependent tariff, and according to the distance-dependent tariff when the frequency is higher. For the selection of the right tariff (distance or time) it is usual to arrange a frequency comparison about twice per travelled meter, i.e. with high repetition frequency. In practice, this means that if it is desired to arrange a central computer to carry out the calculation of the fare, radio transmission would be necessary twice per driven meter or the corresponding time interval. This would lead directly to unacceptable consequences from the point of view of radio communication.